Message box in loop to save file does not appear - excel

Question

I have an Excel spreadsheet that should be saved on the desktop when the User presses a button. For this I use the following VBA to check if the file already exists on the Desktop:
Sub SaveFileOnDesktop()
Do
New_Filename = Application.InputBox("Please type in name for new file?")
If New_Filename = False Then Exit Sub
If Len(Dir("C:\Users\" & Environ("Username") & "\Desktop\" & New_Filename & ".xlsm")) = 1 _
Then MsgBox ("File alreday exists. Please change file name.")
Loop Until Len(Dir("C:\Users\" & Environ("Username") & "\Desktop\" & New_Filename & ".xlsm")) = 0 Or New_Filename = False
ActiveWorkbook.SaveCopyAs "C:\Users\" & Environ("Username") & "\Desktop\" & New_Filename & ".xlsm"
MsgBox ("File saved successfully on desktop.")
End Sub
Now when the User enters a file name that already exists on the desktop the loop continues. Once the user enters another name the loop does stop. This functionality works fine so far.
The only issue I have is that the MsgBox ("File alreday exists. Please change file name.") does not appear if the user enters an exisitng name into it.
What do I have to change in my code so the message box appears?

Answer 1

This cannot be True, thus the MsgBox does not appear:
If Len(Dir("C:\Users\" & Environ("Username") & "\Desktop\" & New_Filename & ".xlsm")) = 1
The length would be at least 10+, if the file is present or 0 if it is not present. 1 cannot be achieved.
To make it appear, write:
If Len(Dir("C:\Users\" & Environ("Username") & "\Desktop\" & New_Filename & ".xlsm")) > 1
or even:
If Len(Dir("C:\Users\" & Environ("Username") & "\Desktop\" & New_Filename & ".xlsm"))